This invention relates to methods and apparatus for the deposition of thin films and, more particularly, to the deposition of such films by means of plasma enhanced reactive deposition.
It has been known for many years that thin film deposition processes and the properties of the deposited films themselves can be improved by allowing energic ions to impinge on the growing surface of the film being deposited; this is due to an energy transfer between the energic ions and the so-called "adatoms" of the thin film being deposited. This increases the surface mobility of the adatoms and allows them to migrate more easily to the preferred lattice sites.
A convenient way of effecting energic ion impingement is to operate the deposition process in a plasma present in the process chamber, for example in sputtering, plasma enhanced chemical vapour deposition (PECVD) and ion assisted evaporation processes.
Critical to the success of such plasma deposition processes is the presence of a high ion density in the plasma, for example of the order of, or preferably in excess of 1.times.10.sup.12 cm.sup.2.
However presently available processes do suffer from certain disadvantages, in particular that they generally require to be operated at relatively high substrate temperatures, commonly of the order of 250.degree. C. or above, to achieve the necessary film thicknesses and properties.
The present invention provides an improved plasma deposition process which generally allows for the deposition to be effected at reduced substrate temperatures whilst maintaining, and in many instances, improving the film characteristics.